The present invention relates to a power control circuit and, for example, relates to a power control circuit including a current measurement circuit that measures a current flowing through a power transistor.
A power transistor is widely used today as an element that passes a current through a load requiring a large current. As the power transistor, an element using a bipolar transistor or an element using MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used, for example. Particularly, IGBT (Insulated Gate Bipolar Transistor) is commonly used.
For example, an inverter circuit, a battery charger or the like using a power transistor measures a current flowing through a load and performs feedback control of the power transistor by using a measured current value. In the case of driving a motor by using an inverter circuit, for example, because a torque generated by the motor is proportional to a current, a current flowing through the motor (coil) is fed back in order to obtain a desired torque. Further, in a battery charger, a current flowing through a battery is fed back in order to prevent a current exceeding a specified value from flowing to the battery.
For the detection of a current, a shunt resistor, a current transformer, a Hall element, a magnetoresistive element and the like are mainly used. In the case of using the shunt resistor, a resistor is inserted into a path through which a load current flows, and voltages at both ends of the resistor are measured. Although current measurement using the shunt resistor can be made with a low cost, because heating due to Joule loss in the resistor occurs, it is used for applications with relatively small current consumption such as electric home appliances.
In applications that pass a relatively large current such as industrial equipment, electric vehicles and hybrid vehicles, a current transformer, a Hall element, a magnetoresistive element and the like are used. The current transformer is a device that includes a primary coil inserted into a path through which a load current flows and a secondary coil magnetically coupled to the primary coil, and reads a voltage generated at the secondary coil. The Hall element is a device that reads a voltage generated by passing a current different from a load current in a magnetic field where a load current is generated. The magnetoresistive element is a device that places an element whose resistance value varies depending on a magnetic field where a load current is generated, and reads a voltage generated when passing a current through the resistor.
Further, the technique that measures a current flowing through a load by using a Hall element and performs feedback control of a current flowing through a load with the measured current value is disclosed in Japanese Unexamined Patent Application Publication No. 2004-72807.